Since I read Alan Stoddard’s words: His hands are his instruments, and what more delicate or refined instrument is there on this earth? The hands communicate (1), I have been interested in Manual Therapy. Manual, hands-on techniques commonly applied by physical therapists are based on Cyriax, Osteopathic, Mennell, Maitland, and Kaltenborn-Evjenth approaches. All of these comprehensive evaluation and treatment concepts are using techniques to decrease symptoms, to increase mobility, to activate, reeducate, and strengthen muscles while restoring and maintaining optimal function of the neuromusculoarticular system (1-12). Passive joint mobilization is a part of the manual therapy. The purpose of this paper is to discuss the rationale for mobilization as a manual technique.
The word mobilization is used loosely to describe the different kind of manual treatment techniques in manual therapy. Soft tissue mobilization (massage, active muscle relaxation, passive stretching), joint mobilization (basic, advanced, thrust, as well as traction and gliding), neural tissue mobilization, and mobilizing exercises are included into techniques to increase mobility. Traction, vibrations and oscillations are used as the techniques relieving symptoms (7,9). The other way to characterize mobilization as a passive movement technique is to divide it in two. First, the techniques to relieve pain and restore pain-free functional movement including passive oscillation and sustained stretching, and secondly, the technique to maintain a functional range of joint movement (6).
In the general sense, mobilization is seen as any movement technique that when applied to musculoskeletal tissue mobilizes them and may be localized or regional (13). Typically, in physical therapy mobilization is understood as a repetitive passive movement of varying amplitudes of low velocity applied at different parts of the range of motion depending on the effect desired. Manipulation, when precisely described, involves a high velocity thrust of small amplitude performed at the limit of available movement (14). Some authors use manipulation as a synonymous with manual therapy covering all the techniques applied in manual therapy (15). Manipulative techniques in osteopathy include soft-tissue techniques, articulator techniques, and specific techniques (3).
From here on, I am using the term mobilization as a passive joint movement of varying amplitudes of low or high velocity applied at different parts of the range of motion depending on the desired effect. By that mean, I include specific joint mobilization (traction or gliding), specific joint manipulation (thrust), and vibration, oscillation techniques under the term mobilization and exclude soft tissue treatments (massage, muscle stretching) and active mobilization (mobilizing exercise). In the other words, mobilization here means manual passive joint mobilization that may be applied as slow mobilization, quick manipulation, or vibration and oscillation. These techniques are claimed to decrease pain, relax muscles, increase circulation, increase nutrition, and increase mobility (1-3,6-9,13-16).
Pain is a subjective, unpleasant perception of the noxious stimulus (17). It always indicates some degree of tissue dysfunction and potential tissue damage (18,19). Nociceptors are terminal endings of finely myelinated or unmyelinated afferent peripheral nerve fibers. They are selectively sensitive to mechanical, thermal, or chemical stimuli (17,18). Most of the neuromusculoarticular tissues are innervated, and therefore a possible source of pain. Only a superficial layer of articular cartilage, intra-articular menisci, nucleus pulposus, inner layers of the annulus fibrosus and synovial tissue does not have direct nociceptive innervation (17,20), although nociceptors are found in the facet joint plical synovial tissue (21). The sensitivity of a tissue to the noxious stimulus correlates to the density of nociceptors of that tissue (17).
The density of nociceptors is high in the fibrous capsules of the synovial joints (19). Based on controlled studies using comparative local anesthetic blocks more than 50% of all chronic neck pain after a whiplash injury was localized to zygapophyseal joints (22). The lumbar zygapophyseal joint pain was found to be the source of low back pain from 15% (23) to 40% (24) of cases. The internal lumbar disc disruption is the most studied source of disc pain (25). In this condition the nucleus pulposus is biomechanically degraded and radial fissures develop into the annulus fibrosus. Diagnosed by discography and CT, pain was found to be coming from internal disc disruption in just under 40% of cases: stimulation of adjacent discs did not provoke patient’s symptoms in these cases (26).
Although favored by clinicians, the entry of muscle pain is difficult to accept. Clinically muscles are reacting to deeper stimuli. Nevertheless, a pathophysiological model for the cause of muscular tension and pain in occupational pain syndromes and chronic musculoskeletal pain syndromes suggests that metabolites produced by (static) muscle contractions stimulate group III and group IV muscle afferents, which activate gamma-motoneurones. The gamma-motoneurones influence the stretch sensitivity and discharges of secondary and primary spindle afferents. Increased activity in the primary muscle spindle afferents enhances the muscle stiffness, which leads to further production of metabolites in muscle. Increased activity in secondary spindle afferents, which project back to the gamma system, continues a build in the second positive feedback loop which may perpetuate the condition with less support from activity in group III and group IV muscle afferents (27). On the other hand, the tissue oxygen tension has shown to be markedly higher in those with tense muscles than those with no increased muscle tension. Hypoxia is not the result of increased muscle tension, but results from an oversupply of oxygen demanded by the muscle, leading to increased capillary perfusion and rising oxygen tension (28). The role of the muscle as a source of musculoskeletal pain is not confirmed.
Acute compression of a normal peripheral nerve usually does not cause pain but numbness, paresthesia, motor weakness, and related symptoms. Mechanical compression of a normal spinal nerve root also seems to induce similar sensory and motor impairment without associated pain. Mechanical factors can induce the intraneural inflammation in the nerve roots. This may lead to hyperexcitability of nerve tissue and pain. Mechanical lumbar nerve root compression does not seem to be a sole cause of leg pain and/or neurologic dysfunction. The inflammatory reaction in the neural and perineural tissues is the most likely explanation of the pain (29).
Headaches are a common complaint that can be produced by many sources and causes. Any musculoskeletal primary cause of pain that activates the trigeminocervical nucleus can provoke a headache. The trigeminocervical nucleus is the essential nociceptive nucleus of the head, throat and upper neck. All nociceptive afferents from the trigeminal, facial, glossopharyngeal and vagus nerves and the C1-C3 spinal nerves ramify in this single column of gray matter. Therefore, the origin of headache may be located in any of the structures innervated by the trigeminal, VII, IX, X cranial nerves and the upper three cervical spinal nerves. Extra-cranial distribution of C1-C3 spinal nerves includes carotid arteries, atlanto-occipital and atlanto-axial joints, alar and transverse ligaments, C2-3 zygapophyseal joints, C2-3 intervertebral disc, prevertebral and post-vertebral muscles, trapezius, and sternomastoid muscle (30,31).
Decreased joint mobility
Immobilization leads to decreased joint mobility. Decreased passive mobility is accompanied with reduced filling volume of the joint cavity and raised intra-articular pressure during movement (32). A significant loss of water and glycoaminoglycans (GAG) takes place without significant loss of collagen mass in periarticular connective tissue. This leads to decreased spacing and lubricating properties as well as to anomalous collagen cross-links (33-36). Cross-links between fibers inhibit their normal gliding and then leads to restricted joint movement and stiffness (37). Six weeks of immobilization is enough to cause a significant limitation to joint mobility (38). Any situation that led to an immobilization, can cause some degree of degenerative changes in musculoskeletal system (39).
Restricted joint mobility is an articular phenomenon, remaining unchanged under anesthesia. Blockage in an articular movement results in reflex changes in related tissues (15). Intra-articular meniscoids, faulty movement patterns and posture, trauma, and reflex action (15,21,40,41) may block joint mobility. Synovitis, rheumatoid conditions, degeneration, capsular fibrosis, adhesions, bony ankylosis, and plane anomalies are factors that associated with joint dysfunction (42). An osteopathic spinal lesion is a condition of impaired mobility in an intervertebral joint in which there may or may not be altered positional relations of adjacent vertebrae. The characteristics of the spinal lesion in addition to restricted movements are pain, tenderness, swelling of surrounding soft tissues, muscular contraction and skin changes (3). A somatic dysfunction involves musculoskeletal tissues as well as related vascular, lymphatic, and nervous tissues. Pain, weakness, stiffness, numbness, headache, dizziness, nausea, etc., are often accompanied with soft tissue and functional changes. Typical soft tissue changes are altered tissue tension, elasticity, shape, texture, color, temperature, etc. Functional changes include impaired strength, endurance, coordination and impaired mobility of joints, soft tissues, neural and vascular elements (9).
Clinically, a restricted joint mobility effects to a quality and a quantity of the movement (15). Both may be assessed by a clinician. The quantity of the movement can be measured with an instrument but the assessment of the quality of the movement requires seeing and feeling. Passive movement should be free, smooth and not dependent on the speed. When the passive movement is carried out from the point of first resistance to the final stop, the type of resistance may be sensed (7,9). This end feel information defines the type of tissue restricting the motion, and therefore aids in the treatment planning. Passive translatoric, non-voluntary joint movements (joint play) are used to get additional information of the movement abilities of the joint tested (6,7,9).
Pain modulation by mobilization
All synovial joints of the body are provided with four types of receptor nerve endings. Three out of four types are mechanoreceptors, which are responding to tension changes in the tissue they are embedded. Type IV receptors are nociceptors. They are normally inactive but can be stimulated by an abnormal amount of tissue tension or by chemical substances. They are found throughout the entire thickness of the joint capsule and between the fibers of the ligament. They are absent from synovial tissue, intra-articular menisci and articular cartilage. The nociceptive afferents impulses are transmitted polysynaptically to the alpha motoneurons in the local motoneurone pools of the muscles related to that joint in question. Therefore, they are able to produce abnormal reflex activity in the muscles when irritated (43).
The receptor population varies in different joints and in different regions of each joint capsule. Type I mechanoreceptors are located in the outer layers of the fibrosus joint capsule. Their density is the greatest in the apophyseal joints of the cervical spine. They are active in the beginning and at the end of the range of tension and function as static and dynamic mechanoreceptors holding postural reflexogenic effects (slow adapting, low threshold). Type II mechanoreceptors are embedded in deeper layers of fibrosus capsules and in intra-articular fat pads. These low threshold rapidly adapting receptors are active in mid range of tension, functioning as dynamic mechanoreceptors. Type III is confined to the surface of intrinsic and extrinsic joint ligaments. They are absent from the ligaments of the spine. They have a high threshold and behave as slowly adapting mechanoreceptors. These dynamic receptors are activated only at the end of the range by high tension. The articular mechanoreceptor afferent fibers from all types transmit polysynaptically to fusiforme motor neurons within the central nervous system. They have reflexogenic influence on muscle tone and on the excitability of stretch reflex in voluntary muscles (43). Through this connection joint mobilization can produce reflex muscle tone changes by motor unit facilitation and inhibition.
The gate control theory of pain describes the mechanism, which afferent and descending pathways can modulate sensory transmission by inhibitory mechanisms in the central nervous system. One of the oldest methods of pain relief is hyperstimulation analgesia produced by peripheral activation of mechanoreceptors. A brief stimulus may relieve chronic pain for long periods, sometimes permanently. “Closing the gate” in the brainstem reticular formation may relieve pain. Prolonged relief may require the disruption of reverberatory neural circuits responsible for the “memory” of pain. Hyperstimulation normalizes neural function, which helps to prevent the recurrence of the abnormal neural activity (44,45). Type I, II and III mechanoreceptor fibers transmit to the posterior horn of the spinal cord. They synapse with neurons of apical spinal nucleus that connect with presynaptic terminals of the nociceptive afferent fibers located in basal nuclei. Because the apical interneurons release an inhibitory transmitter substance at the synapse, nociceptive impulses are inhibited. Therefore, joint mobilization can modulate the pain by presynaptic inhibition of nociceptive afferent activity (16).
Most of the studies measuring the effectiveness of manipulation or mobilization in pain reduction compare them to the other treatment stimulating peripheral sensory transmission. This is not the best way to study the effect of manipulation and mobilization on pain. Anyway, not only the effect on pain, but on total functional ability should be studied. On the other hand, manipulation or mobilization should never be the only treatment given to the patient; it should always be combined with other treatments.
Shekelle et al (46) reviewed over 50 articles looking for the efficiency of spinal manipulation as a treatment of low back pain. Their analyzed 25 controlled trial studies finding that spinal manipulation is of a short-term benefit in some patients, particularly those with uncomplicated, acute low back pain. Manipulation, as well as mobilization, has shown to decrease the low-back pain patient’s disability measures by 80% over the 2-week course of follow up (47). Manipulative treatments have also shown to settle down benign mid dorsal and/or unilateral chest pain (48). Osteopathic manipulation has not only a significant short-term effect to low-back patient’s recovery, but a suggestion of a long-term benefit (49). Headaches of cervical origin are often treated by mobilization. Mobilization is effective in decreasing frequency, duration and intensity of headaches. Even chronic headaches associated with neck pain, difficulty concentrating, nausea, light sensitivity, and other symptoms can be treated successfully (50). A single quick manipulation is more effective than a slow mobilization in decreasing pain in patients with mechanical neck pain. Both treatments increase range of motion in the neck to a similar degree (51).
Mobilization and joint mobility
A loss of physiological stress alters the morphologic, biochemical, and biomechanical characteristics of various components of synovial joints. It can lead to a generation of fibrofatty connective tissue within the joint space, adhesions between synovial folds, adherence fibrofatty connective tissue to cartilage surfaces, atrophy of cartilage, “ulceration” at points of cartilage-cartilage contact, disorganization of cellular and fibrillar ligament alignment, weakening of ligament insertions sites, regional osteoporosis, increased force requirement for joint cycling, and increased ligament compliance. Load-to-failure and energy-absorbing capacity of the bone-ligament-bone complex reduces to about one-third of normal. Collagen turnover and formation of collagen cross-links increases. Proteoglycan content and water content are reduced (52).
All this needs to be taken into consideration when applying mobilization techniques. Mobilization may be applied to normalize nutrition and lubricative properties of the joint, or to improve mobility. Passive repetitive translatoric movement, traction or gliding, to the first resistance is used to improve nutrition, circulation and lubrication in the joint structures. Gentle slow mobilization when taken far enough into resistance is used to obtrude cross-link formation and generate change. The goal of the passive mobilization is to reverse the negative changes in the joint, and normalize arthrokinematic gliding and rolling movement. The increased gliding will normalize osteokinematic rotation and enable the use of active physiological stress in rehabilitation (53).
Systematic literature review of cervical manipulation and mobilization supports at least short-term benefits for neck and headache patients (54). Cervical mobilization improves segmental mobility and normalizes biomechanics of the cervical spine (51,55,56). Spinal manipulation has shown to improve outcome in low-back pain patients (46). Glenohumeral joint mobility can be improved by mobilization (57), but joint mobilization can also normalize the mechanics of the shoulder and therefore decrease pain, increase range of motion, and normalize function in variety of shoulder diagnoses (58). Glenohumeral joint mobilization with exercises is superior to improve joint mobility and function when compared to exercises without mobilization (59). Positive effect of joint mobilization to range of motion is demonstrated in metacarpal-phalangeal joint. Mobilization increases range of motion, alters joint mechanics, and counteracts the effects of immobilization (60).
Summary and conclusions
Physiological stress, load and movement are essential for the development, maintenance, and continuing health of the musculoskeletal tissues. Inactivity, faulty movement patterns and posture, trauma, or decease can result tissue changes with symptoms and dysfunction. Healing, the tissue response that can restore tissue structure and function, can be facilitated by loading and motion.
Joint mobilization is important part of the treatment stimulating tissue healing. Oscillation, vibration, and repetitive traction or gliding mobilization to the first resistance modulates pain, decreases muscle tone, increase nutrition in the tissues, and reverses the effects of decreased mobility. Slow mobilization and oscillation, when applied beyond the first resistance increases joint mobility and normalizes physiological movement allowing better function of the musculoskeletal system. Quick manipulation is effective way to alter muscle tone, modulate pain and reorganize the collagen cross-links.
Therefore, joint mobilization is an important and almost always necessary treatment technique in the beginning of the rehabilitation process reducing pain, maintaining nutrition, and improving mobility. Mobilization allows early use of physiological active movement for tissue facilitation. However, unskillful mobilization may cause additional tissue trauma. The ability to control force, direction, speed, and duration of the movement applied is essential in mobilization. Ability to localize the joint or tissue area that is in need of mobilization is fundamental for safe and effective application of the joint mobilization. Learning the manual skill to control the passive movement takes a long time and a great effort.
Only in very rare cases joint mobilization is the only treatment technique needed to stimulate healing and to normalize function. Joint mobilization should always be combined with other treatment techniques. When specific mobilization is applied as a part of the therapy, a significant difference to conventional therapy is found. A significant difference in favor of manual therapy and specific mobilization is shown in sick leave, pain score, disability rating, recovery score, drug consumption, quality of life, and prevalence of common symptoms. Also a significant difference in objective findings, assessed by blinded, independent and unbiased orthopedic surgeons is demonstrated in favor of mobilization and manual therapy when compared to traditional physical therapy. The results of the long-term follow-up studies indicate the long-term efficacy of manual therapy and specific mobilization (61,61,63,64).
As physical therapists, we have many well-demonstrated neurophysiological, biochemical, biomechanical and functional reasons to learn and use mobilization as a part of rehabilitative process. However, more research to define quantitative understanding of the mechanisms of action, dose-responsiveness, special tissue effects and their controls need to be done. More we know, better we can take care of our patients. The gift of manual skills should be shared: the hands communicate.
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